1. Field of the Invention
The invention relates to a protection path reservation method for use in a transmission system applied to a backbone network, etc. More specifically, the present invention relates to a protection technique protecting a transmission path in an optical transmission system known as an all-optical network from a failure.
2. Description of the Related Art
A recent information transmission system usually connects a plurality of nodes in a mesh-like manner via links to form a mesh network. To allocate a transmission resource of the mesh network to a plurality of communication paths, a method for retrieving an optimum route by means of a routing algorithm has been applied up to now. In recent years, a network has received much attention, wherein the network transparently transmits an optical signal as it is without converting the optical signal into an electrical signal at a node and also without converting its wavelength. Such a network is referred to as an all-optical network, and can provide a plurality of logical bands on the links.
In a network of this type, each transmission path is protected from failures by using protection paths which are set with correspondence to each transmission path. In a dedicated protection system that is one of the systems for protection, dedicated protection paths are assigned to each transmission path. Therefore, the dedicated protection system has to secure transmission bands corresponding to all the protection paths in the network and falls into a difficulty in efficient use of the transmission bands. In comparison to such a system, a shared protection system in which a plurality of protection paths share the same transmission band is superior in band use efficiency.
In the shared protection system, the plurality of protection paths reserve the same band (in a competitive situation), and when a line failure occurs, one protection path among them uses the reserved band. However, an occurrence of a node failure results in that a plurality of protection paths are involved with a relief of traffic. Accordingly, the occurrence of the contention among reservations for bands among the protection paths makes a protection function of no use. That is, the contention among the reservations disables the shared protection system from dealing with the node failure. To achieve protection against the node failure, a mechanism to avoid the contention among the reservations for the using transmission bands is required.
Jpn. Pat. Appln. KOKAI publication No. 2003-258851 discloses a path protection method in a transmission system. However, this reference does not cover the all-optical network.